Larissa, Chris and Rachel hope everyone had a Merry Christmas and a Happy New Year! Despite the demands of irrigation, hopefully people managed a break over the holiday period. Moving into the new year, cotton crops across the Darling Downs are looking great.

Much of the irrigated cotton is now flowering or will over the next few weeks. Dryland, as mentioned in previous editions, is much more variable, with some only now approaching squaring while others are stacking on fruit.

Growth of crops – a quick look out in the field

Crops on the Downs are in various stages of growth and development, with members of the CSD Extension team finishing off establishment counts at the same time as conducting first flower assessments for the trial program in mid-December. Much of the crop in the region will be flowering through January and it is important to remember that flowering is a critical period of crop development. It is where the yield potential of your crop is established. The length of the flowering period, conditions and stresses encountered during this flowering period will determine the production and retention of bolls, and also the fibre quality of your crop.

• CSD offer a number of digital tools that may be applicable at this time of year: CottonTracka® is a great CSD tool that can be utilised to monitor and optimise your crops performance. We have added in a couple of pictures of crops we are tracking as part of our trials program.

Figure 1: Snapshot of STEFF tool for first flower. STEFF algorithm and climate analysis model offers guidance to growers and agronomists in predicting first flower dates.

Drilling down into the Downs, most crops have achieved first flower by 16 – 17 nodes (6-7 vegetative nodes though this does vary from farm to farm. Height is a lot harder to pin down. Some crops have been below average leading into flowering, while others are above average, as per the example in Figure 2. Both are irrigated crops planted in early October, with both flowering in mid-December. The crops also have similar retention, with their major difference being that they are located on opposite sides of the valley - one near Brookstead and the other near Miles. It is important to keep track of your crop and manage for your farm.  

Figure 2: Node and height progression of two irrigated crops on the Darling Downs at first flower. The left chart is of a crop located near Brookstead and the right near Miles. Node production is similar at 17 nodes while heigh varies.

Other metrics to keep track of over January as the crop progresses is boll numbers. While not always a glamorous task, boll counting is a more reliable indicator of yield potential in a cotton crop than retention percentages, because it directly measures the number of bolls, which is the primary determinant of yield. Retention percentages, while useful, only provide information about the proportion of fruiting sites that remain on the plant at a given time and don’t reflect the absolute number of developing bolls. It is conceivable that crops can have low retention and high numbers of bolls resulting in excellent yields. 

• CSD’s STEFF (Simulated Time to Estimated First Flower) is a useful tool to help you estimate the date of first flower.
• BARRY assists Australian cotton growers and consultants to assess their yield potential at key growth stages and utilises the vast dataset of the CSD Ambassador Network and Variety Trial programs.

Wilt - Fusarium found

As many know Fusarium Wilt can often cause problems on the Darling Downs. While we are currently not seeing wider spread incidents or it affecting entire fields, it is important to be vigilant. There have been cases this year of Fusarium appearing early and of it outright killing plants, even prior to flowering.

What is it? Fusarium is a soil-inhabiting fungus that causes Fusarium wilt, a significant disease affecting cotton crops in Australia. The specific pathogen responsible is Fusarium oxysporum f. sp. Vasinfectum. Once introduced, Fusarium wilt is almost impossible to eradicate and failure to control disease build-up can result in fields becoming unsuitable for cotton production.  

Key visual indicators are

• Yellow mottling on leaves

• Brown discoloration in the woody part of the stem

• Plants may die back from the top and potentially regrow from the base later in the season

• Symptoms can appear as individual plants or small patches, often in tail drains or low-lying waterlogged areas 

Prevention is the best course of action with farm hygiene being key: Thoroughly pressure wash machinery on sealed surfaces with waste water retention capacity and implement "Come Clean! Go Clean!" protocols for all farm traffic, including contractors. If Fusarium is on farm, avoiding crop stresses such as over-irrigation and excessive nitrogen application may help reduce its effects and retaining cotton residues on the soil surface as long as possible before incorporation to reduce its effects for the next season.

Insects - activity on the down low

As crops move into peak flowering and early boll fill, continued vigilance is essential. Key insects moving about now are mirids. They have caused some retention loss and tipping of plants across the region. Curiously we have observed Heliothis egg lays and moths moving about in crops. No major damage apart from some holes in leaves but will be interesting to keep an eye out if populations increase.

Coming up - events

To showcase the new XtendFlex® varieties, CSD intend to conduct field walks in the coming months. CSX 1320B3XF will take centre stage as it gears up for commercialisation. These visits aim to provide a snapshot of varietal performance. Dates and locations will be finalised over the coming weeks. Keep an eye out for further details or contact one of us in the New Year to find out more.

If you feel like either you or your staff would benefit from a little bit of extra cotton knowledge in 2026, then it is worth remembering that the new CRDC Cotton Course will be run by the University of Sydney from 10-12 March this year. Currently there is a discount on the course and there are still places available.  

Regards, CSD Extension and Development Agronomist’s Larissa Holland, Chris Barry and Rachel Russell 

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